1. Field of Invention
The invention relates to an organic electroluminescent display device and, in particular, to a self-charging organic electroluminescent display device.
2. Related Art
The structure of an organic electroluminescent display 100 is shown in FIG. 1. It is mainly comprised of a substrate 110, a positive electrode 120, an organic electroluminescent film 130, a metal negative electrode 140, a glass packaging cover 150, and a packaging resin 160. When a voltage is imposed on the organic electroluminescent display, electrons and holes flow from the negative electrode 140 and the positive electrode 120 into the organic electroluminescent film 130 and combine into excitons there to emit light.
The structure of an organic solar cell is shown in FIG. 2. It is mainly comprised of a substrate 210, a transparent positive electrode 220, an organic solar energy absorption film 230, a metal negative electrode 240, a glass packaging cover 250, and a packaging resin 260. When sunlight shines on the solar cell, the organic solar energy absorption film 230 absorbs the solar energy and excites singlet excitons, i.e. an electron-hole pair. The electric field imposed on the positive electrode 220 and the metal negative electrode 240 separates the electron-hole pair into free electron and hole. They are connected to an external loop to generate electricity.
The structure of an inorganic solar cell is shown in FIG. 3. It is mainly comprised of a substrate 310, a transparent positive electrode 320, an inorganic P-type semiconductor 330, an inorganic N-type semiconductor 340, a metal negative electrode 350, a packaging resin 360, and a glass packaging cover 370. When sunlight shines on the solar cell, ionizations occur at the PN semiconductor junction to form electron-hole pairs. The generated electrons and holes flow toward the negative and positive electrodes, respectively. They are collected at the electrodes to provide a voltage. Finally, a conductive wire is used to excite singlet excitons, i.e. an electron-hole pair. The electric field imposed on the positive electrode 220 and the metal negative electrode 240 separates the electron-hole pair into free electron and hole. They are connected to an external loop to generate electricity.
The organic electroluminescent display is combined with an organic solar cell to form a light-emitting device. The U.S. Pat. No. 6,028,327 discloses a similar idea, as shown in FIG. 4. The structure of the organic electroluminescent display 1 includes a positive electrode 22, organic films 23, 24, and a negative electrode 25 formed on a substrate 21. The inorganic solar cell 2 is formed from a stack of three sets of solar cell units 3, 4, 5. It is combined with the light-emitting device using the negative electrode 25 as the common negative electrode. The films 25, 28, 31 in the inorganic solar cells 3, 4, 5 are negative electrodes, and the films 27, 30, 33 are positive electrodes. The inorganic films 26, 29, 32 are solar energy absorption films. The positive electrode 33 is covered with a second substrate 34. The inorganic solar cell 2, external circuits 11, 12, a control switch 15, and a battery 16 form a loop. When the inorganic solar cell absorbs the sunlight and converts it into electrical energy, the electrical energy is stored in the battery 16 via the external loop. When the organic electroluminescent display 1 needs electrical power, the electricity flows from the battery 16 into the light-emitting device via the circuits 11, 13 and the switch 15. Therefore, when the light-emitting device and the solar cell are combined using a common negative electrode, the solar cell cannot be charged at the same time when the display is in use.
Since the solar cell and the organic electroluminescent display have similar manufacturing processes, the solar energy absorption film or the organic electroluminescent film can be directly formed on the substrate of the positive electrode by coating or vacuum evaporation. Afterwards, the module is formed on the negative electrode by vacuum evaporation. The process finished after packaging.